1. Field of the Invention
The invention relates to a control apparatus and method for a vehicular automatic transmission. More particularly, the invention relates to technology for executing a neutral control for as long as possible while ensuring durability of a frictional apply device in the automatic transmission.
2. Description of the Related Art
A known control apparatus for a vehicular automatic transmission, such as that disclosed in JP(A) 9-32917, includes a frictional apply device and a control portion. The frictional apply device serves as an input clutch, increasing or decreasing torque transmitted from the engine depending on whether it is applied, slipping, or released. The control portion places the automatic transmission in a substantially neutral state by reducing an application load on the frictional apply device when the vehicle is stopped. This operation, known as neutral control, reduces the engine load which improves fuel efficiency.
When a certain amount of torque is allowed to be transmitted to the frictional apply device during the neutral control, however, the temperature of the frictional apply device increases excessively, which may reduce the durability of the frictional apply device. The reason for this excessive rise in temperature is that the neutral control has been continuously executed for equal to, or greater than, a predetermined period of time or that a transmitted torque that is greater than an expected value has been applied to the frictional apply device. In order to prevent the temperature of the frictional apply device from rising, the foregoing technology sets the time for which neutral control can be continuously executed using only the continuation time of the neutral control as the determination criteria. In consideration of durability in the most severe circumstances, this technology makes the time for which neutral control can be continuously executed relatively short.